Social workers failed to act on formal warnings about the behaviour of a highly disturbed 11-year-old boy who raped a child two years his junior, a serious case review has found.

Sunderland council's children's services did not properly assess the boy's needs or the risk he posed, despite the concerns of health professionals about his mental instability and sexual behaviour.

Child X attacked a nine-year-old boy in 2009 having lured him into a bedroom to play a computer game. He admitted rape at Newcastle crown court and was sent to a detention centre for four and a half years.

The review summary report said the council had failed to take child X into care despite repeated requests and evidence of serious behavioural problems. "Sunderland children's services social care ... consistently failed in their statutory duties to safeguard child X."

In common with several recent serious case reviews, the inquiry found that it was not lack of resources that caused the failure but insufficent shared planning, record keeping and communication between social workers, NHS, schools and police services. But the report was clear that the ultimate responsibility lay with Sunderland children's services' failure to take a lead role.

Two letters about X's behaviour were sent to protection officials by a child psychiatrist just weeks before the attack, urging them to take action. But these were ignored.

The inquiry report summary sketched out the chaotic and unstable family life of X, himself a victim of abuse and maltreatment. He had come to London in 2001 as a refugee and his father was killed in a suspected drugs feud a year later.

While living in London X was referred by his school to child mental health services. The inquiry report said the boy had witnessed domestic violence from an early age and had a "poor attachment" to his mother.

The pair were "dispersed" to Sunderland, where concern over X's family circumstances "accelerated". His mother became involved in a relationship "punctuated by separations and domestic violence".

The NHS treated the boy for physical and emotional problems, while his behaviour meant he was in regular contact with the police and the local youth offending team. He was referred to social services on a number of occasions.

During this time both his mother and stepfather were receiving support from mental health services, drugs and alcohol teams and probation workers, although the inquiry report summary notes that "they were inconsistent in their take up".

The family of Child X told the inquiry they "were not given sufficient help" by the many public agencies who had been involved in their son's life in London and the north-east. But the inquiry concluded that "in reality there were a large number of resources going in to help the family".

Sentencing child X in 2009, Judge Beatrice Bolton suggested the attack could have been avoided had the council moved him from his family. The council said it "at the time it was felt this was not the most appropriate course of action".

Child X's attack on the nine-year-old took place while he was awaiting trial after being accused of sexually assaulting two 10-year-old girls and an 11-year-old girl. Those charges were later dropped.

The Sunderland city council leader Paul Watson said: "We acknowledge that things could have been done better. We've listened and learned from what went wrong and we've put in place in a series of measures, including extra training, resources and investment."

The council said that, given the complexity of the case and the number of professionals involved in it, no single individual could be held culpable and as a result no staff face disciplinary action as a result of the review findings. Two social workers who worked with the family have since died, and other staff have left the council.